The present embodiments relate to an ultrasonic diagnostic apparatus and others that can three-dimensionally visualize a temporal change in blood flow dynamic state in, e.g., an organ which is a diagnostic imaging target by using microbubbles as an ultrasonic contrast agent, and more particularly to an ultrasonic diagnostic apparatus, an ultrasonic image processing apparatus, and medical diagnostic imaging apparatus that can easily observe information of, e.g., a dynamic change in blood flow or fine angioarchitectonic with high visibility.
Ultrasonic diagnostic imaging is easy to use since a state of heartbeat or fetal movement can be obtained in real-time display by a simple operation, i.e., just applying an ultrasonic probe from a surface of a body, examinations can be repeatedly conducted because of high safety, a system scale is smaller than that of any other diagnostic device of X-ray, CT, or MRI, and bedside examinations can be also easily performed. Further, the ultrasonic diagnosis has no influence of radiation exposure as different from X-rays, and it can be used in obstetrics, home medical care, and others. Particularly, in recent years, an agitation probe (a probe that enables ultrasonic scan of a three-dimensional region by mechanically agitating a row of one-dimensionally aligned ultrasonic oscillators) or a two-dimensional array probe (a probe that enables ultrasonic scan of a three-dimensional region by a row of ultrasonic oscillators aligned in a matrix form) can be utilized to perform real-time three-dimensional scan (which is also called “four-dimensional scan”).
Furthermore, in recent years, an intravenous administration type ultrasonic contrast agent has been productized. In the ultrasonic diagnostic imaging, performing contrast imaging using such a contrast agent enables acquiring various kinds of information. For example, in case of a primary liver cancer, a differential diagnosis about benign and malignancy and others can be carried out by complementarily using blood flow information of an arterial phase or blood flow information of a portal phase. Moreover, when the contrast imaging is performed after an RFA treatment, an ablated area is not stained, and hence this imaging is also applied to an effect judgment. Additionally, an imaging method for intravenously injecting an ultrasonic contrast agent to enhance a blood flow single in an examination of, e.g., a heart and a liver and thereby evaluating a blood flow dynamic state has been also suggested. A replenishment method and micro flow imaging are representative examples of an imaging method for evaluating the blood flow dynamic state.
The replenishment method is a technique by which characteristics that air bubbles of a contrast agent collapse are exploited, (a) a dynamic state of the air bubbles filling a scan cross section is observed under radiation of a low acoustic pressure, (b) the radiated acoustic pressure is switched to a high acoustic pressure to collapse the air bubbles in the cross section (in an irradiated volume in a precise sense), and (c) a state of the air bubbles that again flow into the cross section is observed.
In general, the contrast imaging is characterized in that a fine blood flow that cannot be visualized by, e.g., color Doppler can be visualized. On the other hand, only a small quantity of bubbles are present in the fine blood flow. Therefore, staining is non-steadily effected. The micro flow imaging is a technique that characteristics of such contrast imaging and a contrast agent are utilized and non-steadily visualized bubbles are temporally superimposed and displayed to more clearly visualize a fine blood flow configuration. When executing the micro flow imaging, there is a restriction that a patient must hold his/her breath for a fixed time and an examiner such as an operator must fix a probe. As a technology that alleviates this restriction, a technology that corrects movement of a target region by image processing has been also suggested (see, e.g., Patent Document 2).
In such contrast imaging, for example, dynamic information such as a staining start time phase (namely, which corresponds to a bubble arrival time), a time phase that staining achieves a peak (a peak time), a Wash-In time defined by an arrival time—a peak time of bubbles, a Wash-Out time defined by a time at which the bubbles flow out to a vein—the peak time is acquired spatially (i.e., at each position). It may be preferable for these pieces of dynamic information to be observed as moving images in some cases. For example, in case of a liver, a tumor is nourished with arterial blood, and a normal parenchyma is nourished with portal blood. Therefore, effecting observation using moving images enables putting a clock time that the contrast agent reaches a tumor region ahead of those in peripheral regions, thereby visually confirming how the tumor begins to be stained earlier than the other regions.
On the other hand, in the observation of moving images of the dynamic information, since a temporal change at each position must be retained in a user's head, it cannot be necessarily said that this observation is objective. Further, there is also a problem that the observation requires a certain amount of time. To solve these problems, a two-dimensional parametric imaging technology that enables observing dynamic information by using one two-dimensional image has been suggested. According to this technology, for example, a maximum value of a temporal change in luminance in each pixel is determined as a peak time, or a threshold value that is not affected by, e.g., noise is provided, a calculation of, e.g., determining a first time at which the threshold value is exceeded as an arrival time is performed to obtain temporal information. Furthermore, a two-dimensional image whose color tone is changed in accordance with each position is displayed based on a value of the obtained temporal information. It is effective to combine this technology with the above-described Micro Flow Imaging or movement correction technology, and utilization at clinical scenes in the future is expected.
However, in the two-dimensional parametric imaging, since two-dimensional image data (tomographic data) is used, there is a limit in representation of spatial continuity of a blood flow. It is difficult to recognize, e.g., a blood vessel having a configuration in a depth direction. For example, a blood vessel orthogonal to a tomographic image is substantially represented as a dot.
On the other hand, in case of observing a blood flow dynamic state (a temporal change in blood flow), when a plurality of pieces of volume data having different time phases are observed, the number of dimensions of the observation range increase by one as compared with a conventional diagnosis based on a two-dimensional image (a tomographic image), an observation time increases, and a problem that the construction (storage) of temporal change information also becomes ambiguous in an operator's head occurs.
Therefore, it can be considered that performing parametric imaging using time-series volume data (four-dimensional parametric imaging) is effective. However, in regard to three-dimensional visualizing method of temporal information such as an arrival time, a method that is effective in clinical practice has not been suggested. That is because simply three-dimensionally carrying out the two-dimensional parametric imaging cannot appropriately process temporal information concerning a depth direction. Particularly, in recent years, a contract imaging function has been introduced into ultrasonic diagnostic apparatuses that enable four-dimensional scan. Therefore, establishing a four-dimensional parametric imaging technique to enable three-dimensional observation of a dynamic blood flow state has a high clinical value and is strongly demanded.
In view of the above-described problems, it is an object of the present embodiment to provide an ultrasonic diagnostic apparatus, an ultrasonic image processing apparatus, and a medical diagnostic imaging apparatus that enable easily observing information such as a dynamic blood flow change or fine angioarchitectonic with high visibility based on the four-dimensional parametric imaging.
To achieve this object, the present embodiment takes the following measures.
In general, according to one embodiment, there is provided an ultrasonic diagnostic apparatus comprising: a data acquisition unit configured to scan a three-dimensional region in a subject having a contrast agent injected therein over a predetermined period by using ultrasonic waves and to thereby acquire ultrasonic data concerning the three-dimensional region over the predetermined period; a volume data generation unit configured to generate first volume data in each time phase in an analysis period by using the ultrasonic data concerning the three-dimensional region over the analysis period in the predetermined period and to generate second volume data indicative of contrast agent temporal information about the analysis period and third volume data indicative of a contrast agent characteristic amount at each position in the three-dimensional region in the analysis period; and an image generation unit configured to generate a projected image by using the second volume data and the third volume data.